The invention relates generally to ultrasonic surgical instruments and processes and more particularly to methods and apparatus for facilitating the performance of surgical procedures such as cauterization of large blood vessels or simultaneous soft tissue dissection and coagulation of small vessels through the use of a precisely controlled ultrasonically vibrating scalpel.
The use of an electric scalpel or a laser as a surgical instrument with the dual function of simultaneously effecting the incision and hemostasis of soft tissue by cauterizing tissues and blood vessels while cutting are known. Electrosurgery using such instruments, however, employs very high temperatures to achieve coagulation, causing vaporization and fumes as well as splattering, which increases the risk of spreading infectious diseases to operating room personnel. Additionally, the use of such instruments often results in relatively wide zones of thermal tissue damage.
Cutting, shattering and drilling instruments with ultrasonic drive mechanisms in non-surgical fields are known. Additionally, conventional surgical instruments utilizing the capacity of ultrasonic vibrations to cut or shatter a wide range of living tissues such as the soft tissue found in cataract surgery as well as bone chips or the like in orthopedics, are also well known.
One of the problems associated with such ultrasonic cutting instruments is uncontrolled or undamped vibrations and the heat as well as material fatigue resulting therefrom. In an industrial application, such problems can be dealt with by simply turning off the instrument when it is not in contact with the workpiece. In an operating room, however, such practice is neither practical nor acceptable. That is to say, in the latter environment precise cutting and heating control must be provided in order to prevent thermal tissue injury and scalpel fracture.
Known devices have attempted to solve the heating problem by the inclusion of cooling systems with heat exchangers or the like. In one known system, for example, the ultrasonic cutting and tissue fragmentation system requires a cooling system augmented with a water circulating jacket as well as requiring means for irrigation and aspiration of the cutting site. Another system uses ultrasonic cutting of soft tissue wherein the ultrasonic cutting instrument requires the delivery of cryogenic fluids to the cutting blade.
In accordance with my invention, there is provided a method and apparatus for overcoming the foregoing and other problems associated with conventional electric, laser and ultrasonic surgical incising/cautery devices. The exemplary embodiments disclosed include the "power on demand" control feature of causing a surgically sharp cutting instrument, such as a scalpel blade, or other surgical instrument such as a dull cautery blade to automatically shift its operation between an unloaded or idle state and a loaded or cutting state, and vice versa, depending on whether or not the instrument is in contact with tissue.
Such contact can be determined by monitoring parameters such as ultrasound driving current or impedance in response to the dampening of the vibration which occurs upon tissue contact.
When in the loaded or cutting state the blade is supplied with longitudinal back and forth movement at ultrasonic frequencies and at a selectable cutting power level. Such ultrasonic activation of the blade, although increasing the efficiency of cutting, generates heat as the mechanical energy of the accelerating moving blade is converted to thermal energy. Under such circumstances, the localized heat creates a very narrow zone of thermal coagulation that reduces or eliminates bleeding. The zone is narrow or limited since temperature elevations are transient and heat is produced only at the narrow contact point of the blade edge. Moreover, since the power level is selectable as a percentage of full power, a range of cutting/coagulation control levels is available to the surgeon for selection depending on the nature of the tissue encountered as well as other factors.
When in the unloaded or idle state, power is still transmitted to the instrument for the purpose of monitoring operating parameters, but such power is at a reduced or low level, thereby minimizing heat build-up. Elimination of such heat build-up is important since at high power levels the vibrating blade will become very hot when not in contact with tissue or other physiological medium if allowed to continue to run in air at high power. When the entire blade is hot, the zone of thermal injury is less controlled and excessive thermal tissue injury results in an extended healing period as well as excessive scarring. Furthermore, excessive heating of the blade resulting from undamped ultrasonic vibration may lead to stress fractures in the instrument and injury to nearby personnel.
Accordingly, it is an important feature of my disclosed exemplary methods and apparatus that power be continuously applied to the device so that operating parameters can be continuously or periodically monitored for detected changes in response to damping of the vibrations upon tissue contact or detected changes in response to undamped vibrations or oscillations upon withdrawal of the blade from tissue contact. Detection of such changes are used for the automatic application of a controlled amount of power to the ultrasonic surgical instrument, such as the application of an increased selected level of cutting power to the blade in going from the idle state to a cutting state when tissue contact is sensed, and the rapid reduction in power applied to the blade when withdrawal of such contact is sensed.
In a further exemplary embodiment, the disclosed methods and apparatus include a coagulation mode wherein power of a selectably high level is applied for a short time for coagulating relatively large bleeders. This mode is implemented, for example, by the user selecting the duration of high coagulation power application and the time of initiation through the use of a switch or the like and thereafter tamponading the bleeder with the back or edge of a blade.
In a still further exemplary embodiment, the disclosed methods and apparatus include a system wherein the selection of operating parameter threshold levels is such that the surgical device will not inadvertently switch from the idle state to the loaded or cutting state when the blade is immersed in blood or other body fluid but not in contact with tissue. Such selection of threshold levels eliminates splattering and ultrasonic atomization of the fluids and assures delivery of cutting power only when the scalpel blade makes contact with tissue in the act of cutting or coagulating. Careful selection of appropriate system operation parameters must also be made in determining the point at which the system is to be powered down to the idle or unloaded state in order to prevent overheating of the acoustic system; such overheating occurs when high power is delivered to the surgical instrument in an undamped condition.
These and further objects and advantages of the present invention will become apparent upon reference to the following specification, appended claims and draWings.